Parr Il. Secr. ui. §2.] CRETACEOUS. 821 
telli, A. lewesiensis (= part of A. varians zone); the third bed (2 feet, 
9 inches), also abundantly fossiliferous, contains among other forms 
Peliastes clathratus, Hemiaster Morrisiit, Terebratula rigida, Rhynchonella 
mantelliana, Ammonites rhotomagensis, A. varians ; this and the two under- 
lying beds are regarded as comprising the zone of Ammonites rhotomagensis 
and A. varians ; the fourth bed, or zone of Holaster subglobosus (148 feet), 
contains among its most characteristic fossils Discoidea cylindrica, Holaster ~ 
subglobosus, Goniaster mosaicus, and in its upper part Belemnites plenus ; the 
fifth bed, or zone of Belemnites plenus, consisting of yellowish white 
gritty chalk (4 feet), forms a well-defined band between the Grey Chalk 
and the overlying lower subdivision of the White Chalk (Turonian) ; it 
contains few fossils, among which are Belemnites plenus, Hippurites 
(Radiolites) Mortom, Piychodus. 
Recent researches by the Geological Survey in Cambridgeshire have 
‘shown that in that region the Chalk Marl is covered by a band of harder 
stone (Totternhoe Stone), passing up into sandy and then nearly puie 
white chalk, and that these strata, equivalents of the Chalk Marl and 
Grey Chalk, are probably separated by a paleontological and strati- 
graphical break from the next overlying (Turonian) member of the 
series.! According to the original classification of M. Hébert, this zone 
of Belemnites plenus is placed at the base of the Turonian group; by 
Dr. Barrois it is made the summit of the Cenomanian. The latter view 
receives support from the evidence of a break and considerable denu- 
dation above this zone in England. 
Turonian (Lower White Chalk without flints)—The White Chalk of 
England and north-west France forms one of the most conspicuous 
members of the great Mesozoic suite of deposits. It can be traced from 
Flamborough Head in Yorkshire across the south-eastern counties to 
the coast of Dorset. Throughout this long course its western edge 
usually rises somewhat abruptly from the plains as a long winding 
escarpment, which from a distance often reminds one of an old coast-line. 
The upper half of the deposit is generally distinguished by the presence 
of many nodular layers of flint. With the exception of these enclosures, 
however, the whole formation is a remarkably pure white pulverulent 
dull limestone, meagre to the touch, and soiling the fingers. Composed 
mainly of crumbled foraminifera, urchins, molluscs, &c., it must have 
been accumulated in a sea tolerably free from sediment, like some of the 
foraminiferal ooze of the existing sea-bed. There is, however, no evi- 
dence that the depth of the water at all approached that of the abysses 
in which the present Atlantic globigerina-ooze is being laid down. 
Indeed, the character of the foraminifera, and the variety and associa- 
tion of the other organic remains, are not like those which have been 
found to exist now on the deep floor of the Atlantic, but present rather 
the characters of a shallow-water fauna. Moreover, the researches of 
M. Hébert have shown that the chalk is not simply one continuous and 
homogeneous deposit, but contains evidence of considerable oscillations, 
and even of occasional emersion and denudation of the sea-floor on which 
it was laid down. The same observer believes that enormous gaps 
occur in the upper Cretaceous series of the Anglo-Parisian basin, some 
of which are to be supplied from the centre and south of France 
(postea, p. 826). 
1 A. J. Jukes-Browne, Geol. Mag. 1880, p. 250. 
